1. Field of the Invention
The present invention relates to an antireflection film, a polarizing plate, and a display device comprising the same.
2. Description of the Related Art
In general, an antireflection film is disposed on the outermost surface of display devices such as cathode-ray tube (CRT) devices, plasma display panels (PDP), electroluminescent display devices (ELD) and liquid-crystal display devices (LCD). This is for preventing contrast reduction or image reflection caused by external light reflection on the displays, by reducing the reflectance owing to the principle of optical interference thereon.
The antireflection film of the type is generally produced by forming, on a support, functional layers (e.g., hard coat layer, antiglare layer, light-diffusive layer, high-refractive layer) and further a low-refractive layer having a suitable thickness thereon. For realizing its low reflectance, the material for the low-refractive layer is desired to have a refractivity as low as possible. Since the antireflection film is disposed on the outermost surface of displays, it is desired to have high scratch resistance. In order to realize high scratch resistance of thin films having a thickness of 100 nm or so, the films must have high mechanical strength by themselves and must be adhesive to underlying layers.
JP-A 2003-222704 describes adding a silane coupling agent to a low-refractive layer material comprising a fluoropolymer thereby to enhance the adhesiveness of the layer to the underlying layer and to improve the scratch resistance of the layer. It further describes adding a silane coupling agent also to the underlying hard coat layer material thereby to further enhance the adhesiveness between the upper and lower layers and to greatly improve the scratch resistance of the upper layer. However, the silane coupling agent has a low boiling point and its use is therefore problematic in that the agent may vaporize during the coating and drying step of forming the intended layer. Another problem with the agent is that the agent must be added in an excessive amount thereof in consideration of its vaporization and therefore a layer of stable quality is difficult to form when the agent is used.
A method of reducing the vaporization of the agent is described in JP-A 2004-170901, which comprises previously reacting a silane coupling agent by the use of an acid catalyst or a metal chelate catalyst to form a hydrolyzate and/or a partial condensate thereof, and adding it to a coating liquid to thereby reduce the vaporization of the agent in the coating and drying step of forming a layer. However, when a silane coupling agent is added to the underlying hard coat layer material according to the method, then it gives a problem in that the necessary adhesiveness, scratch resistance and optical properties could not be stably expressed depending on the degree of the hydrolysis and/or the partial condensation of the silane coupling agent.